The proposed research is a study of the bacteriophages of Bacteroides fragilis with major emphasis on: 1. types of phages, 2. DNA homology among phages and between phage and hosts, 3. ability of phages to carry out transduction of antibiotic resistance, 4. use of the phages for clinical identification of B. fragilis subspecies fragilis. The phages will be characterized as to host range, serological relatedness, morphology (electron microscopy), and type of nucleic acid. The DNA phages will be compared in regard to nucleotide sequences by DNA homology experiments. Homology experiments will also be used to detect host DNA in the phages. This information will enable us to select those phages that are most likely capable of transduction. Transduction of tetracycline resistance will be attempted first since resistance to this antibiotic has increased dramatically in recent years in B. fragilis. Although this increase in tetracycline resistance has been most noted in B. fragilis subspecies fragilis, the most pathogenic subspecies, the less pathogenic subspecies of B. fragilis found in the human colon have increased in resistance at an equal rate. The bacteriophages that we have isolated for B. fragilis can be transferred from one subspecies to another at low frequency, but it appears that there is enough specificity so that an identification scheme can be developed for recognition of the most pathogenic subspecies.